d2c PID-Conversion

Question

Christoph Fleischmann 2024-7-22

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2139361-d2c-pid-conversion

评论： Christoph Fleischmann 2024-7-23

采纳的回答： Walter Roberson

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Hi,

I'm trying to convert a discrete-time PID-controller to a continuous-time PID using the d2c function.

c_discrete = pid(4.406,0.0114,0.0112,0,0.0050) %Kp, Ki, Kd, Tf, Ts
c_continuous = d2c(c_discrete) 

But I keep getting the following Error:

Error using DynamicSystem/d2c (line 108)

The "d2c" conversion failed because the result cannot be expressed as a PID controller.

Does anyone have an Idea, where my mistake is?

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Answer 1

Walter Roberson 2024-7-22

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https://ww2.mathworks.cn/matlabcentral/answers/2139361-d2c-pid-conversion#answer_1488951

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That error is given when Tf < Ts, and apparently exists in order to avoid getting complex-valued outputs.

Your Tf is 0, certainly less than Ts.

Example with Tf > Ts

c_discrete = pid(4.406,0.0114,0.0112,0+0.01,0.0050) %Kp, Ki, Kd, Tf, Ts
c_discrete =
 
              Ts               1     
  Kp + Ki * ------ + Kd * -----------
              z-1         Tf+Ts/(z-1)

  with Kp = 4.41, Ki = 0.0114, Kd = 0.0112, Tf = 0.01, Ts = 0.005
 
Sample time: 0.005 seconds
Discrete-time PIDF controller in parallel form.
c_continuous = d2c(c_discrete) 
c_continuous =
 
             1            s    
  Kp + Ki * --- + Kd * --------
             s          Tf*s+1 

  with Kp = 4.41, Ki = 0.0114, Kd = 0.00808, Tf = 0.00721
 
Continuous-time PIDF controller in parallel form.

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Walter Roberson 2024-7-22

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c_discrete = pid(4.406,0.0114,0.0112,0,0.0050) %Kp, Ki, Kd, Tf, Ts
c_discrete =
 
              Ts            z-1 
  Kp + Ki * ------ + Kd * ------
              z-1           Ts  

  with Kp = 4.41, Ki = 0.0114, Kd = 0.0112, Ts = 0.005
 
Sample time: 0.005 seconds
Discrete-time PID controller in parallel form.
c_continuous = d2c(c_discrete, d2cOptions(method='matched')) 
Error using DynamicSystem/d2c (line 108)
The "matched" method of the "d2c" command cannot be used for models with negative real zeros with odd multiplicity.